The present invention relates to the fabrication of cutting elements for use in rock drilling, machining of wear resistant metals, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies which comprise a polycrystalline diamond layer attached to a cemented metal carbide stud through processing at ultrahigh pressures and temperatures.
In the following disclosure and claims, it should be understood that the term polycrystalline diamond, PDC, or sintered diamond, as the material is often referred to in the literature, can also be any of the superhard abrasive materials, including, but not limited to synthetic or natural diamond, cubic boron nitride, and wurtzite boron nitride as well as combinations thereof. Also, cemented metal carbide refers to a carbide of one of the group IVB, VB, or VIB metals which is pressed and sintered in the presence of a binder of cobalt, nickel, or iron and the alloys thereof.
This application is related to composite or adherent multimaterial bodies of diamond, cubic boron nitride (CBN) or wurtzite boron nitride (WBN) or mixtures thereof for use as a shaping, extruding, cutting, abrading or abrasion resistant material and particularly as a cutting element for rock drilling.
As discussed in U.S. Pat. No. 4,255,165, a cluster compact is defined as a cluster of abrasive particles bonded together either (1) in a self-bonded relationship, (2) by means of a bonding medium disposed between the crystals, or (3) by means of some combination of (1) and (2). Reference can be made to U.S. Pat. Nos. 3,136,615; 3,233,988 and 3,609,818 for a detailed disclosure of certain types of compacts and methods for making such compacts. The disclosures of these patents are hereby incorporated by reference herein.
A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. A bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. It is, however, highly preferable to form the bond at high temperatures and high pressures comparable to those at which the cluster compact is formed. Reference can be made to U.S. Pat. Nos. 3,743,489; 3,745,623 and 3,767,371 for a detailed disclosure of certain types of composite compacts and methods for making same. The disclosures of these patents are hereby incorporated by reference herein.
As discussed in U.S. Pat. No. 5,011,515, composite polycrystalline diamond compacts, PDC, have been used for industrial applications including rock drilling and metal machining for many years. One of the factors limiting the success of PDC is the strength of the bond between the polycrystalline diamond layer and the sintered metal carbide substrate. For example, analyses of the failure mode for drill bits used for deep hole rock drilling show that in approximately 33 percent of the cases, bit failure or wear is caused by delamination of the diamond from the metal carbide substrate.
U.S. Pat. No. 3,745,623 (reissue U.S. Pat. No. 32,380) teaches the attachment of diamond to tungsten carbide support material with an abrupt transition therebetween. This, however, results in a cutting tool with a relatively low impact resistance. Due to the differences in the thermal expansion of diamond in the PDC layer and the binder metal used to cement the metal carbide substrate, there exists a shear stress in excess of 200,000 psi between these two layers. The force exerted by this stress must be overcome by the extremely thin layer of cobalt which is the common or preferred binding medium that holds the PDC layer to the metal carbide substrate. Because of the very high stress between the two layers which have a flat and relatively narrow transition zone, it is relatively easy for the compact to delaminate in this area upon impact. Additionally, it has been known that delamination can also occur on heating or other disturbances in addition to impact. In fact, parts have delaminated without any known provocation, most probably as a result of a defect within the interface or body of the PDC which initiates a crack and results in catastrophic failure.
One solution to this problem is proposed in the teaching of U.S. Pat. No. 4,604,106. This patent utilizes one or more transitional layers incorporating powdered mixtures with various percentages of diamond, tungsten carbide, and cobalt to distribute the stress caused by the difference in thermal expansion over a larger area. A problem with this solution is that "sweep through" of the metallic catalyst sintering agent is impeded by the free cobalt and the cobalt cemented carbide in the mixture.
U.S. Pat. No. 4,784,023 teaches the grooving of polycrystalline diamond substrates. This patent specifically mentions-the use of undercut (or dovetail) portions of substrate ridges, which solution actually contributes to increased localized stress. Instead of reducing the stress between the polycrystalline diamond layer and the metallic substrate, this actually makes the situation much worse. This is because the larger volume of metal at the top of the ridge will expand and contract during heating cycles to a greater extent than the polycrystalline diamond, forcing the composite to fracture at the interface. As a result, construction of a polycrystalline diamond cutter following the teachings provided by U.S. Pat. No. 4,784,023 is not suitable for cutting applications where repeated high impact forces are encountered, such as in percussive drilling, nor in applications where extreme thermal shock is a consideration.
U.S. Pat. No. 4,592,433 teaches grooving substrates but it does not have a solid diamond table across the entire top surface of the substrate. While this configuration is not subject to delamination, it cannot compete in harsh abrasive applications.
U.S. Pat. No. 5,011,515 teaches the use of a sintered metal carbide substrate with surface irregularities spread relatively uniformly across its surface. The three dimensional irregularities can be patterned or random to control the percentage of diamond in the zone that exists between the metal carbide support and the polycrystalline diamond layer. This zone can be of varying thickness.
U.S. Pat. No. 4,109,737 teaches the use of a pin with a reduced diameter hemispherical projection over which a diamond layer is directly bonded in the form of a hemispherical cap. The polycrystalline diamond layer receives greater support from the hemispherical shape to make the surface more resistant to impact.